<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>

</body>
<script>
    var sum = 100;
    var money = ''
    var bank = prompt('请输入您要的操作: \n 1.存钱 \n 2取钱 \n 3.显示余额 \n 4.退出\n');
    if (bank == 1) {
        prompt('请输入您要存的钱')
    } else if (bank == 2) {
        prompt('请输入您要取的钱')
    } else if (bank == 3) {
        prompt('您的余额为')
    } else {
        alert('您已退出银行')
    }
</script>

</html>